Snail Mucus Increases the CO₂ Efflux of Biological Soil Crusts

Biological soil crusts (hereafter, biocrusts) are communities of microorganisms that regulate key ecosystem processes such as water distribution, soil erosion, and nutrient cycling in drylands worldwide. The nature of biocrust function can be influenced by multiple environmental factors, including climatic conditions (for example, precipitation), interactions with plants, and anthropogenic disturbances. Animal regulation of biocrust function has received less research attention, focusing primarily on livestock trampling and to a much lesser extent on biocrust consumption by mesofauna. Deposition of animal waste products, carcasses, and other body secretions such as mucus may also affect biocrust function. Yet, this novel regulatory pathway, to our knowledge, has never been empirically tested. Our goal was to begin bridging this knowledge gap by exploring how snail mucus affects biocrust CO₂ efflux—using two distinct biocrust communities and three snail species. We found that snail mucus increased the CO₂ efflux of both cyanobacteria-dominated and lichen/moss-dominated biocrusts. However, the magnitude of snail mucus effects on biocrust CO₂ efflux varied between snail species—possibly due to species-level differences in snail diet. Our study highlights a novel interaction between animals and biocrusts and suggests that even small quantities of animal-derived nutrients can have important consequences for biocrust carbon dynamics.